Polish SessionLimit

- Move to the web.authentication.session package since it is only needed
by web.authentication.session elements and does not access any other web
element itself.
- Add Kotlin support
- Add documentation

Issue gh-16206

web/src/test/java/org/springframework/security/web/authentication/session/ConcurrentSessionControlAuthenticationStrategyTests.java

@@ -34,7 +34,6 @@ import org.springframework.security.authentication.TestingAuthenticationToken;
 import org.springframework.security.core.Authentication;
 import org.springframework.security.core.session.SessionInformation;
 import org.springframework.security.core.session.SessionRegistry;
-import org.springframework.security.web.session.SessionLimit;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;

web/src/test/java/org/springframework/security/web/authentication/session/SessionLimitTests.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.springframework.security.web.session;
+package org.springframework.security.web.authentication.session;
 
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;